1. Field of the Invention
The present invention relates to a holding device for the end part of an optical fiber and a method for using the device, and more specifically, to an optical fiber end part holding device for determining the position of an optical fiber end part when optical fiber end parts are aligned in contact and joined by thermal welding using an optical fiber fusion splicer, and the method by which this is performed.
2. Description of the Related Art
In conventional technology, when joining optical fibers, a fusion connection method is used in which, after the ends of the optical fibers to be connected are aligned in contact, they are thermally welded together. In order to reduce connection loss occurring when optical fibers are connected, the axial centers of both optical fibers must be precisely matched.
To achieve this alignment, an optical fiber end part holding device 101 as shown in FIG. 1 is used, in which both optical fibers 103 to be joined are arranged in a V-groove 107 provided in a base 105. Further, a pressuring member 109 is used, the sloped faces of which form a V-shape, in order to fit into the V-groove 107. The axial centers of the optical fibers 103 are precisely matched as the optical fibers 103 are pressured into the V-groove 107 by the flat lower face 111 at the end part of the pressuring member 109. When this occurs the appropriate degree of gap S between the sloped face of the pressuring member 109 and the V-groove 107 can be maintained as the width W of the lower face 111 of the pressuring member 109 is matched to the size of the optical fibers 103.
There are a number of different types of optical fibers 103 that may be connected, the external diameters of which differ according to their use. A first holding method of the conventional art for holding optical fiber ends of optical fibers 103 having different external diameters in the lower part of the V-groove 107 involves changing the pressuring member 109.
For example, FIG. 1 shows the condition in which a large diameter optical fiber 103 is held by a pressuring member 109 the width W of the lower face 111 of which is broad, while FIG. 2 shows the condition in which a small diameter optical fiber 103 is held by a pressuring member 109 the width W of the lower face 111 of which is narrow. In this way the width W of the lower face 111 can be changed to match the external diameter of the optical fiber 103 by changing the pressuring member 109 and the optical fiber 103 can be definitively held in the lower part of the V-groove 107.
However if a small diameter optical fiber 103 is held by the holding mechanism for a large diameter fiber as that shown in FIG. 1, a gap T opens between the lower part of the V-groove 107 and the lower face 111 of the pressuring member 109 as shown in FIG. 3, thus the optical fiber 103 cannot be held at the bottom part of the V-groove 107.
Further, if a large diameter optical fiber 103 is held by the holding mechanism for a small diameter fiber as that shown in FIG. 2, the gap S between the sloped face of the pressuring member 109 and the sloped face of the V-groove 107 becomes large as shown in FIG. 4A, causing the pressuring member 109 to become displaced as shown in FIG. 4B or inclined as shown in FIG. 4C such that the optical fiber 103 can not be precisely held at the lower part of the V-groove 107. Accordingly, it is necessary in order to definitively hold optical fibers 103 having differing external diameters at the lower part of the V-groove 107, to change the pressuring member 109 to match the external diameter of the optical fiber 103.
A second example of conventional technology for an optical fiber end part holding device, such as that disclosed in Japanese Unexamined Patent Application Publication No. 2003-14974, does not involve changing the pressuring member, but provides a method for holding optical fibers having different external diameters at the lower part of a V-groove.
Referring to FIGS. 5A and 5B, a concave part 113 is provided in the center part of a V-groove 107 provided in a base 105, while a convex part 117 is provided in the center part of a fiber clamp 115 that provides a pressuring member, such that this convex part 117 fits together with the concave part of the V-groove 107. In this way, even when an optical fiber 103 is displaced from the center part of the V-groove 107, the convex part 117 of the fiber clamp 115 fits to the concave part 113 of the V-groove 107, pressing the optical fiber 103 to the lower part of the V-groove 107 such that the optical fiber 103 can be guided to move to the center of the V-groove 107 and held.
A third example of conventional technology for an optical fiber end part holding device, such as that disclosed in Japanese Unexamined Patent Application Publication No. 2004-4350 also, does not involve changing the pressuring member, but provides a method for holding optical fibers having different external diameters at the lower part of a V-groove.
As shown in FIG. 6, a part at the rear part of the V-groove 107 provided in the base 105 is formed at a different level such that the part at the rear part of the V-groove 107 is not as deep as the other part. There are two types of pressuring member for this arrangement, a fiber clamp 119 for a large diameter optical fiber held in the frontal part and a fiber clamp 121 for a smaller diameter optical fiber held in the rear part. These two types of clamp are constructed so as to be independently movable.
A problem that affects the first type of conventional optical fiber end part holding device arises when holding optical fibers 103 have differing external diameters at the lower part of the V-groove 107. In this case, a plurality of types of pressuring member 109 matching the external diameters of the optical fibers 103 must be arranged and work is required to change the pressuring member 109 as the external diameters of the optical fibers 103 change. Thus, a troublesome operation which extends the duration of work time involved must be performed when the optical fibers 103 are connected. Further, a large number of components are required in such a device leading to an increase in the cost of producing the device.
A problem that affects the second type of conventional optical fiber end part holding device is that the width of the lower face of the fiber clamp 115 must be sufficiently narrow for the smallest diameter optical fiber 103, in which case when handling a large diameter optical fiber 103, the fiber clamp 115 can easily drift as shown in FIG. 7A such that the optical fiber 103 cannot be held at the vertex part thereof. Moreover, if the vertex part of the optical fiber 103 is not held, the optical fiber 103 may move upward.
Further, the depth of the V-groove 107 at the concave part 113 of the center part of the V-groove 107 must be shallow in order to hold a small diameter optical fiber 103. Thus, when holding a large diameter optical fiber 103 the optical fiber may move up, as shown in FIG. 7B, as it is not in contact with the V-groove 107 at the concave part 113 of the middle part of the V-groove 107, such that the optical fiber 103 becomes bent by the fiber clamp 115 and may sustain damage.
In this arrangement, if for example the small diameter is φ 125 μm then the maximum diameter that can be worked is 400 μm. However, optical fibers 103 actually have a diameter from φ 80 μm to 900 μm, thus it becomes necessary to provide a plurality of fiber clamps 115 or V-shaped grooves 107.
A problem that affects the third type of conventional optical fiber end part holding device is that when a large diameter optical fiber 103 is held at the frontal, deep V-groove 107 as shown in FIG. 8A, the width of the lower face of the fiber clamp 119 must be matched to the optical fiber 103 having the smallest diameter of the large diameter fibers, and the degree of instability in the holding of the fibers increases proportionally to the increase in the diameter of the optical fiber 103 being held, as shown in FIG. 8B.
Accordingly, when a series of fiber clamps 119 are arranged matching the respective diameters of the optical fibers 103 to be held, the holding parts become longer, the device itself becomes larger and the number of components increases causing a rise in costs.
When handling a small diameter optical fiber 103, as shown in FIG. 8C the fiber is held at the rear part, shallow V-groove 107 and the fiber clamp 121 only, and as the end part of the optical fiber 103 is not pressed at the lower part of the V-groove 107 the end part of the optical fiber 103 may move up.
Also, in the case of the second or third types of conventional optical fiber end part holding devices, the V-shaped grooves 107 for holding the optical fibers as well as the pressuring members are of complex shapes and constructions, resulting in increased production costs.